Formula Support-Duration # of days in a month

Katie,
It's not clear to me how your app knows "which month" when you say how many days occurred in "a month".

hmmm-I guess it doesn't we enter the intake date, the admission date and the discharge date?
But nothing by day-

Katie, For this you will need the field that has the month you are calculating. For example : if someone stayed for 3 months from 15th Jan to 20 April, there are different number of days that person has stayed in each month. 

If you just need to know January (first month from the date admitted) that is fairly simple. Just use the following formula :

ToDays(Min(LastDayOfMonth(Date(Year([BTC Admission Date]),Month([BTC Admission Date]),1)),[BTC Discharge Date]) - [BTC Admission Date])

Katie, if Avinash's answer does not solve your problem, can you give us an example of real data and the real question, just in plain English words, not code.

Okay, I will try that out...
I think you are right tho-I don't have the right data to ask the question.
I really just need to know at the end of each month how many days that client stayed in that month.
But currently only have the date field for admission date and potentially a discharge date (if they discharged) 
I work for a not for profit and I am a "social worker" not a formulas person-but I love this-just having trouble writing formulas...thaks for helping where/when you can...

OK, a clear question in plain English is usually possible to have an answer in Quick Base.

Let's get the question really clear.

You want a report of all Patients who were checked in for at least 1 day last month and how many days they were checked in.  Can you tell me do you count the check in and check out dates at both ends as separate days,  or like a hotel are you just counting "nights

We only count nights (...once I figure this out I need to multiply the days by 24 hours...I add 12 hours for the "last day"...)
each person can stay an unknown duration..

Here is a formula I did  to calculate the storage days in the warehouse last month.   Think of receiving inventory of Clients and then shipping 'em out again! Not so different from rolls of steel coils where the storage fee is per day and they look back to the previous month to cut an invoice for all coils stored last month.  The formula makes use for formula variables for readability

https://help.quickbase.com/user-assistance/formula_variables.html



var date ShipDate = [BTC Discharge Date];

var date ReceivedDate = [BTC Admission Date];


var date FirstDayofPriorMonth = AdjustMonth(FirstDayOfMonth(Today()),-1);

var date LastDayofPriorMonth = LastDayOfMonth($FirstDayofPriorMonth);

var date FirstDayStoredPriorMonth = If(
   $ReceivedDate <= $LastDayofPriorMonth and (IsNull($ShipDate) or $ShipDate >= $FirstDayofPriorMonth), 
                                     Max($FirstDayofPriorMonth, $ReceivedDate));


var date LastDayStoredPriorMonth = If(
             IsNull($ShipDate) and not IsNull($FirstDayStoredPriorMonth), $LastDayofPriorMonth, 
             not IsNull($FirstDayStoredPriorMonth) and $ShipDate >= $FirstDayofPriorMonth, Min($ShipDate,$LastDayofPriorMonth));


var number DaysStoredPriorMonth = If(
    IsNull($ReceivedDate]),0, 
    not IsNull($LastDayStoredPriorMonth), ToDays($LastDayStoredPriorMonth - $FirstDayStoredPriorMonth));


$DaysStoredPriorMonth

Okay-This looks very cool-and at first glance a little over my head. Going to walk the dog and then come back and tackle applying this-I really appreciate your information and will report back with how it goes!!! cheers and have a good night!
Katie

Well copy that formula into a formula numeric field and if we are lucky it will work first try and then I can walk you through it after you walk the dog.